Non-stationary flow around buildings during run-up of tsunami waves on a plain beach

This paper presents an experimental investigation that focuses on some predominant flow features that arise around surface mounted vertical obstacles which are exposed to a transient flow. The flow under investigation is caused by a tsunami-like long wave that climbs up a 1:40 sloping plain beach. In this study the wave height in offshore waters is varied. A single obstacle of 10 cm width as well as side-by-side arrangement of two identical square obstacles with different spacing are considered at an approximate length scale of 1 in 100. The analysis reveals important flow features around the various obstacle configurations. Particular emphasize is laid on the spatiotemporal evolution of the wake angle that linearly increases over time irrespective of the obstacle spacing. The growth rate of the wake angle reciprocally depends on the gap ratio over the investigated range of g† = 0.0 to g† = 3.0

Numerical and experimental study on tsunami run-up and inundation influenced by macro roughness elements

This research study considers long wave run-up experimentally and numerically. At first, an alternative methodology in long wave physical modeling is presented by means of a set of pipe pumps forcing the inflow of a controlled volume of water into a wave channel mimicking a tsunami-like wave shape that is consistently contained by a proportional plus integral plus derivative controller (PID) controller. Arbitrary wave lengths are persistently generated by means of the proposed methodology. First results are compared to tsunami data stemming from conventional experimental configurations with solitary waves as well as with recent numerical modeling results. Comparisons are thoroughly discussed and - in a second step - numerical simulations are accomplished taking the interaction of long wave run-up and macro-roughness elements into account. Four different experimental configurations of macro-roughness elements are carried out while spacing between elements and numbers of obstacle rows are alternated. A fundamental correlation analysis reveals that a correlation of the number of macro-roughness rows, effective area of flow cross section and a grouping factor of different element configurations exists in principle

Interaction of idealized urban infrastructure and long waves during run-up and on-land flow process in coastal regions

This paper reports experimental results of long wave run-up climbing up a 1:40 sloping beach. The resulting maximum run-up is compared with analytical results and a good agreement is found for single sinusoidal waves with uniform wave period and varying amplitude. Subsequently, the interaction with macro-roughness elements on the beach is investigated for different long-shore obstruction ratios. The reduction in wave run-up is expressed by means of a nomogram relating the wave run-up without macro-roughness elements present to those cases where on-land flow is modified by macro-roughness. The presented results mainly focus on a non-staggered and non-rotated macro-roughness configuration. In addition to the run-up reduction, surface elevation profiles on the shore are presented, that address the shock wave generation when the wave tongue approaches the first row of macro-roughness elements.LUHDFGBMB

Experimental study on the performance of coarse grain materials as scour protection

Large scale hydraulic model tests were carried out to investigate the erosive potentials, bed stability and the performance as scour protection of wide-graded quarry-stone material with fractions ranging from 0.063 - 200 mm. Within the two phase test program the material was exposed to several wave spectra during hydraulic model tests in the Large Wave Flume of the Forschungszentrum Küste and additionally to an incrementally increased current in a closed-circuit flume at the Franzius-Institute. As result of the wave load, a maximum scour depth of S/D = 0.161 was observed after 9000 waves with a simulated storm duration of 20 h in model scale. Furthermore, fractional critical shear stresses were determined based on velocity measurements, which indicate highly selective incipient motion of individual fractions under steady current conditions. The selective mobility of this wide-graded material could not be expressed by the Shields approach.Mibau Holding Gmb

NDM-500: OPTICAL TRACKING OF DEBRIS IN EXTREME HYDRODYNAMIC CONDITIONS

Debris impact on structures have been reported and shown to be a major reason for structural failure in many post-mortem site assessments of tsunami devastated communities. However, due to the random nature of the debris motion, determining areas at-risk for debris impact is difficult. This paper presents a novel camera-based object tracking algorithm which allows for the quick and accurate tracking of debris trajectory in highly turbulent flows. The algorithm was used to determine debris motion observed during an experimental program on the displacement of scaled-down shipping containers (debris), carried out by the authors in the Tsunami Wave Basin at Waseda University, Tokyo, Japan. This study evaluated the effect of the initial orientation and number of debris on the time histories of their trajectory, orientation and velocity. The study found that, while random in nature, the motion of the debris was highly repeatable through the various tests conducted. An increase in the number of debris resulted in a higher peak debris velocity. Setting the initial orientation of the long-axis of the debris perpendicular to the flow direction resulted in an earlier and higher peak velocity than in the case of the debris initially oriented parallel to the direction of the flow

Projecting Hydro-Morphodynamic Impacts of Planned Layout Changes for a Coastal Harbor

The macrotidally influenced harbor of Dagebüll on the North Sea coast of Germany features a piled south jetty, for which provided constructive designs are investigated regarding their potential hydro-morphological impacts on the harbor area and adjacent navigational channel. The harbor experiences a steady accumulation of sediment. This results in a reduction of navigational depth and necessitates regular maintenance dredging constituting a cost aspect. A comprehensive field study was conducted, deploying a ridged inflatable boat (RIB) equipped with differential Global Positioning System, a winch for conductivity, temperature, and depth casting as well as sediment and water sampling and an acoustic Doppler current profiler for current profiling. Measurements reveal a tidally governed alternating flow pattern inducing a vortex current inside the harbor basin. Hydrodynamic sea floor grain sorting is detected through sediment sampling. A numerical model cascade is developed and calibrated against available tide gauge and sediment inventory data as well as multibeam survey data and acquired field measurements. The calibrated model cascade is used to simulate layout variants and compare resulting impacts to identify preferable jetty designs

The run-up of long waves : laboratory-scaled geophysical reproduction and onshore interaction with macro-roughness elements

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Physical modelling of arctic coastlines-progress and limitations

Permafrost coastlines represent a large portion of the world's coastal area and these areas have become increasingly vulnerable in the face of climate change. The predominant mechanism of coastal erosion in these areas has been identified through several observational studies as thermomechanical erosion-a joint removal of sediment through the melting of interstitial ice (thermal energy) and abrasion from incoming waves (mechanical energy). However, further developments are needed looking how common design parameters in coastal engineering (such as wave height, period, sediment size, etc.) contribute to the process. This paper presents the current state of the art with the objective of establishing the necessary research background to develop a process-based approach to predicting permafrost erosion. To that end, an overarching framework is presented that includes all major, erosion-relevant processes, while delineating means to accomplish permafrost modelling in experimental studies. Preliminary modelling of generations zero and one models, within this novel framework, was also performed to allow for early conclusions as to how well permafrost erosion can currently be modelled without more sophisticated setups. © 2020 by the authors

Generation and propagation of ship-borne waves - Solutions from a Boussinesq-type model

Ship-borne waves are of significant interest for the design of port and waterway infrastructure and the maintenance of its surrounding environment. Computation of these nonlinear and dispersive waves has mainly been focusing on their near-field generation as a fluid-body interaction problem. This study presents an approach for the computation of ship waves generated by a moving pressure disturbance with phase-resolving and depth-averaged equations. To support a wide range of applicability, the paper deals with the evolution of the vessel wedge compared to an analytical solution for sub-to supercritical speeds and the assessment of wave patterns from a broad range of pressure term dimensions, including cross-references to findings in other studies. The conducted numerical experiments showcase the typical response of a Boussinesq-type model to a simplified moving pressure disturbance and identify the main factors and criteria for ship-wave propagation in the far-field of a vessel. Finally, a unique field dataset underlines the capability of an extended Boussinesq-type model to compute the propagation of vessel waves over an irregular bathymetry.Hamburg Port Authority (HPA)Japanese Society for the Promotion of Sciences (JSPS)EC/FP7/Marie Curie International Outgoing Fellowshi